The invention relates to an electrical circuit arrangement for driving switching power semiconductor components at high voltage potential with a control signal predetermining a switching signal for the power semiconductor component and an output voltage directly controlling the power semiconductor component, a non-controllable semiconductor gate being used for transferring a switching energy.
The power of electrical loads such as, e.g., electric motors, is set by converter circuits which have one or more controllable or non-controllable power semiconductor components such as, e.g., power semiconductor gates. Controllable power semiconductor gates are transistors and thyristors, the diode is non-controllable. The switching state of controllable semiconductor gates is predetermined as a function of input signals, particularly power control signal, speed or rotor position of a motor, by an open- or closed-loop control. The open- or closed-loop control provides the switching signal in the form of logic signals which are converted by driver circuits to the levels and potentials required for driving the power semiconductor components.
In the case of electrical loads needing high supply voltages, e.g. machines connected to single-phase or three-phase AC voltage systems, semiconductor components having a high dielectric strength must be used. Implementation of these as integrated circuits is only possible with great expenditure. The cost for the driver circuit will present a considerable proportion of the total cost of a power controller.
From the prior art, circuit arrangements are known in which a power transistor as controllable semiconductor component determines the load current flowing via its collector-emitter path to a load, and thus the electrical power supplied to the load. Via a driver stage, a gate-emitter voltage of predetermined magnitude is generated, which in switching mode puts the collector-emitter path of the transistor into the conductive state. In this arrangement, the power supply to the driver stage is independent of the switching state of the transistor via a capacitor which is charged up to the operating voltage of a voltage source via a non-controllable semiconductor gate, a diode. To set the power of the load, a control signal A, which is used as input signal to the driver stage, is predetermined as a switching signal in a control section. Since the driver stage is coupled to the high emitter potential of the power transistor, the control signal A must be converted to this voltage potential by a level converter. Such a circuit arrangement is also called a bootstrap circuit.
Such a circuit arrangement corresponding to the prior art is implemented in the driver chip IR2106 by the company International Rectifier (data sheet IR2106, April 1999). To convert the levels of the switching signal, high-voltage-resistant transistors are used here.
The disadvantageous factor in the prior art shown is that both the semiconductor components, via which the capacitor provides the switching energy for the circuit breaker, and the level converter, via which the switching information is transferred, must have a high dielectric strength. The implementation of the level converter, in particular, is associated with high cost expenditure.
The present invention is based on the object of providing a circuit arrangement for driving electronic circuit breakers at high voltage potential which, compared with the prior art, manages with fewer components with high dielectric strength and can be constructed more inexpensively.
According to the invention, this object is achieved in that the non-controllable semiconductor gate is constructed as component with high dielectric strength for transferring the switching signal.
The arrangement according to the invention enables a switching power semiconductor at a high voltage potential to be driven with only one non-controllable semiconductor valve, i.e. a diode, as a high-voltage component. Compared with the prior art, it is possible to omit an expensive level converter since the non-controllable semiconductor gate according to the invention is not used only for the energy transfer as is the case in the above bootstrap circuit of the prior art but, at the same time, also for converting the desired switching state of the power transistor to the high voltage potential. As a particular advantage compared with known circuit arrangements, this results in distinctly lower costs since a level converter would need at least one further controllable high-voltage, and thus expensive, semiconductor component.
The control signal, as input signal to the circuit arrangement according to the invention, determines the variation of an output voltage of a controllable voltage source which is connected in series with the non-controllable semiconductor gate, polarized in the forward direction, and a capacitor. Advantageously, the signal parameters, particularly magnitude, frequency and duty ratio, of the output voltage of the controllable voltage source can be predetermined by this control signal in such a manner that a continuous change in the power consumption of the load is obtained.
A further advantageous embodiment provides that a circuit section is connected in parallel with the capacitor and is supplied by a voltage occurring across the capacitor which stores the switching information and the switching energy.
Due to this circuit combination, i.e. the signal path via the non-controllable semiconductor gate, of two functionally different tasks, in this case the energy supply and the information transfer, there is no necessity for expensive level conversion.
As an extension of this embodiment, a series circuit of a second capacitor and a second non-controllable semiconductor gate, i.e. a diode, but with only little dielectric strength, is provided in parallel with the capacitor. Due to this circuit measure, the second capacitor can handle the task of energy supply whilst the first one stores the switching information and the diode decouples both functions. In this manner, a downstream circuit section can be driven over a greater range.
It is of particular advantage that the circuit section generates an output voltage for driving the power semiconductor component as a function of the capacitor voltage present at the input end. In this arrangement, the output voltage generated is exclusively dependent on the capacitor voltage present at the input of the circuit section. Since this capacitor voltage, in addition to the switching energy, also conveys the information of the switching state according to the invention, the expensive transformation of the switching information to high voltage levels via a level converter can be omitted.
Further suitable embodiments can be found in the subclaims.